Environmental DNA is an emerging tool in conservation for monitoring past and present biodiversity. Environmental DNA transported in river networks offers a novel and spatially integrated way to assess the total biodiversity for whole landscapes and will transform biodiversity data acquisition in ecology.

While rivers cover <1% of the landmasses on earth, they are invaluable for biodiversity and ecosystem services, such as drinking water and energy production. Rivers, because of their characteristic dendritic network structure, also integrate information about the landscape through the collection and transport of sediments, organic matter, nutrients, chemicals and energy.

eDNA is characterized by a complex mixture of nuclear, mitochondrial or chloroplast DNA, and can be intracellular (from living cells) or extracellular. It enables the detection of a species regardless of its life stage or gender. By taking water samples and analyzing them for eDNA, it is possible to show the presence of a species without actually needing to catch individuals or even see them.

It is hypothesized that rivers, through the aggregation and transport of eDNA, act as conveyer belts of biodiversity information that can be used to estimate species richness over broad spatial scales and potentially across the land–water interface.

The relevance of biodiversity sampling with eDNA found in river water is twofold. First, identifying biodiversity hotspots is invaluable for prioritizing global and regional conservation efforts

Second, an eDNA method of biodiversity monitoring in rivers has several advantages in that it is non-lethal for most classically sampled taxonomic groups, minimizes habitat disruption and can assess diversity across the tree of life with a single-field sampling protocol making it extremely cost effective.

Conservation efforts to save biodiversity essentially depend on biological monitoring for obtaining precise data on species distributions and population sizes on a relevant ecological and political time scale. Species monitoring has traditionally relied on physical identification of species by, for example, visual surveys and counting of individuals in the field using distinct morphological characters.

Traditional monitoring techniques have sometimes proven to be invasive on the species or ecosystem under study, such as marine surveys that has relied on highly destructive techniques. Obtaining information of species, populations and communities by retrieving DNA from environmental samples (environmental DNA – eDNA) holds the potential of combating many of these challenges associated with biodiversity monitoring ( Baird and Hajibabaei, 2012 ; Kelly et al., 2014b).

Therefore, demonstrating the power of this tool to monitor biodiversity of important indicator groups in rivers will provide a fast, non-lethal and inexpensive alternative tool compared with classically used methods.